Modulating the visible emission and whispering gallery mode lasing through the self-induced defects in a Ga-doped ZnO tapered microcavity

Abstract

Achieving low-order visible whispering gallery mode (WGM) lasing in monolithic semiconductor microcavities is typically hindered by poorly controlled defect emission and limited dispersion control. We address this by co-designing the gain spectrum and cavity geometry in single, tapered Ga-doped ZnO (GZO) hexagonal microrods grown by vapor-phase deposition. Ga incorporation forms Ga-native-acceptor complexes that red-shift and broaden the deep-level band, creating a tunable 500-600 nm gain window. Concurrently, the built-in diameter gradient (0.73-2.5 µm) deterministically selects WGM order along the same resonator, enabling continuous tuning of WGM order from N = 29 to N = 3-5. Plane-wave analysis and finite-element simulations accurately reproduce the measured path lengths, mode numbers, and linewidth evolution. By uniting defect-state engineering with geometry control in a single cavity, without the use of coupled resonators, plasmonics, or heterostructures, this approach enables the delivery of compact, spatially addressable, low-order visible microlasers for integrated photonics.